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Soft-strain-based sensors are being increasingly used across various fields, including wearable sensing, behavior monitoring, and electrophysiological diagnostics. However, throughout all applications, the function of these sensors is limited because of high sensitivity, high-dynamic range, and low-power consumption. In this paper, we focus on improving the sensitivity and strain range of the soft-strain-based sensor through structure, surface, and sensitive unit treatment. Nanosilver (Ag)-coated hydroxyl-functionalized multi-walled carbon nanotubes (OH-f MWCNTs) were explored for highly acute sensing. With stretching and depositing methods, Ag@OH-f MWCNTs and polydimethylsiloxane (PDMS) are fabricated into a wrinkled and sandwich structure for a soft-strain-based sensor. The electronic properties were characterized in that the gauge factor (GF) = ΔR/R0 was 412.32, and the strain range was 42.2%. Moreover, our soft-strain-based sensor exhibits features including flexibility, ultra-lightweight and a highly comfortable experience in terms of wearability. Finally, some physiological and behavioral features can be sampled by testing the exceptional resistance change, including the detection of breath, as well as facial and hand movement recognition. The experiment exhibits its superiority in terms of being highly sensitive and having an extensive range of sensing.

Microfluid chips integrating with organic electrochemical transistors (OECTs) are useful for manufacturing biosensors with high throughput and large-scale analyses. We report here the utilization of alternating current (AC) electrodeposition to fabricate OECTs in situ on a microfluid chip. With this method, the organic semiconductor (OS) layer with a channel length of 8 ώm was readily prepared without requiring the post-bonding process in the conventional construction of microfluidic chips. Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)/graphene quantum dots (PEDOT:PSS/GQDs) composites with different morphologies, such as microfilms, nanodendrites and nanowires were electropolymerized. The mass transfer process of the electropolymerization reaction was evidenced to be diffusion limited. Morphologies, growth directions, and chemical structures of OS layers could be tuned by the amplitude and the frequency of the AC voltage. Transfer and output characteristic curves of OECTs were measured on the microfluidic chip. The maximum transconductance, on/off current ratio and threshold voltage measured in the experiment was 1.58 mS, 246, and 0.120 V, respectively.

Nowadays, flexible strain sensors applied in the fields of health care and electronic skin have been widely studied and applied. In fact, the temperature characteristic of flexible strain sensors based on metal nanomaterials is rarely concerned. In this work, the ohmic and tensile properties of the flexible strain sensor based on silver nanowires–polydimethylsiloxane were tested and it was found that the sensor has good ohmic characteristics and a maximum gauge factor of 536.98. In addition, the resistance of the sensor was affected little by temperature when the temperature environment of the sensor was changed, and the resistance temperature coefficient of the flexible strain sensor is −1050 ppm/°C. Furthermore, it was found that the sensor was sensitive to minute strain when the sensors were applied to the two application tests of strain and pulse.

The bionic application of electronic skin (e-skin) requires a high resolution close to that of human skin, while its long-term attachment to human body or robotic skin requires a porous structure that is air permeable and enables hair growth. To simultaneously meet the requirements of high resolution and porous structure, as well as improve the sensing performance, we propose a fully 3D printed e-skin with high-resolution and air permeable porous structure. The flexible substrate and electrodes are 3D printed by a direct ink writing extrusion printer. The sensitive material is 3D printed by a self-made low-viscosity liquid extrusion 3D print module. This e-skin has a high sensor density of 100/cm2, which is close to the resolution of the human fingertip skin. The piezoresistive sensor units of e-skin exhibit a highly linear resistance response and a relatively performance consistency between devices. Owing to the porous and breathable structure, better human comfort and mechanical heat dissipation are realized. This high-resolution e-skin is successfully applied to identify small-sized objects with complex contours.

The sensitivity improvement is the choke point of the soft strain sensor’s development. This paper focuses on heightening the soft strain sensor’s sensitivity through changing the sensitive unit’s shape. The sensitive units in shape of square or sine wave with different periods were studied in this work. Silver nanowires (Ag NWs) in excellent electrical conductivity and flexible polydimethylsiloxane (PDMS) were used as sensitive nanomaterials and soft substrate. The soft strain sensor whose sensitive unit is double cycled square wave performs the highest sensitivity whose gauge factor (GF) reaches to 14763.8. Based on the high sensitivity, the sensor was applied on real-time detection of the human expression.

The flexible strain sensor is a fast-moving technology and has been used in many fields. The array design and application based on flexible strain sensors have been the current research hotspots. However, there are few reports on research of acoustic positioning using the flexible sensor array. Herein, we designed and realized the consistent fabrication of a thin-film, acoustic sensor array. The acoustic sensing research of the sensor was demonstrated as well. We used a convenient fabrication method to design a flexible acoustic sensor using silver nanowires coated on a thin polydimethylsiloxane (PDMS) film with mass block-beam structure. The acoustic sensor can record sound within a frequency domain of 20-2000 Hz and volume detection range of 83-108 dB. The sensor's resonance frequency is 380 Hz, horizontal distance sound detection limit is 5 cm, and vertical detection limit is 3.5 cm. We also achieved 360° azimuth detection in two-dimensional space with a detection accuracy of 15°. In three-dimensional space, the flexible acoustic sensor array was designed with two flexible acoustic sensors to detect the position of the sound source. This research first proposes the use of flexible acoustic sensors to test the sound source orientation.

Improvements to the current generation and distribution of electricity via demand side management (DSM) and storage systems are prevalent facing increasing energy demand and environmental implications of electricity generation. In this paper, a multi-level optimization model, which incorporates energy demand scheduler (DS), energy storage (ES) and solar photovoltaic (PV) panels amongst households, was developed so as to lower the peak-to-average ratio (PAR) of energy demand and reduce electricity bills. This model consists of three levels: (1) household consumption optimization (solo opt) using convex programming, (2) grid consumption optimization (base opt) via a game-theoretic framework, and (3) ES/PV allocation optimization using genetic algorithm (GA opt). This framework searches for the optimal allocation of ES/PV in a heterogeneous residential population subdivided into consumer groups by household sizes and income levels. A case study was performed with model parameters determined by referencing state-averaged electricity bills and electricity usage data from Texas, US. The results showed that GA opt can achieve bills savings of ~11% and a PAR reduction from 1.53 to 1.30 by allocating a non-trivial optimal combination of ES/PVs to the households. Another GA opt approach was adopted by minimizing PAR and found that PAR can be effectively reduced from 1.53 to 1.00 with bills savings of ~4%. Most significantly, it was observed that the optimal allocation differs from the free market equilibrium due to positive externalities and synergies when combining DSM together with ES/PVs.

Hg2+ is one of the most universal and severe toxic metal pollutants. Here we reported a high-sensitivity and rapid method for detection of Hg2+. The technique was based on the localized surface plasmon resonance property of gold nanorods. Neither modification of gold nanorods nor separation of analyte was necessary. The longitudinal absorption peak of gold nanorods presented a linear blue shift as Hg2+ concentration increased. The blue shift of longitudinal absorption peak was due to the changes of both aspect ratio and medium dielectric constant. The sensor had a wide linear interval ranging from 285 nM to 8.00 μM, the detection limit was as low as 112 nM, and the sensitivity was 30.48 nm μMμ1, which were comparable to the performance of the modified sensors.

Purpose In this article, we develop a dynamic Bayesian network (DBN) model to measure 3D visual fatigue. As far as our information goes, this is the first adaptation of a DBN structure-based probabilistic framework for inferring the 3D viewer's state of visual fatigue. Methods Our measurement focuses on the interdependencies between each factor and the phenomena of visual fatigue in stereoscopy. Specifically, the implementation of DBN with using multiple features (e.g. contextual, contactless and contact physiological features) and dynamic factor provides a systematic scheme to evaluate 3D visual fatigue. Results In contrast to measurement results between the mean opinion score (MOS) and Bayesian network model (with static Bayesian network and DBN), the visual fatigue in stereoscopy at time slice t is influenced by a dynamic factor (time slice t-1). In the presence of dynamic factors (time slice t-1), our proposed measuring scheme based on DBN is more comprehensive. Conclusion (i) We cover more features for inferring the visual fatigue, more reliably and accurately; (ii) at different time slices, the dynamic factor features are significant for inferring the visual fatigue state of stereoscopy.

The adaptable monitoring of the ubiquitous magnetic field is of great importance not only for scientific research but also for industrial production. However, the current detecting techniques are unwieldly and lack essential mobility owing to the complex configuration and indispensability of the power source. Here, we have constructed a self-powered magnetic sensor based on a subtle triboelectric nanogenerator (TENG) that consists of a magnetorheological elastomer (MRE). This magnetic sensor relies on triboelectrification and electrostatic induction to produce electrical signals in response to the MRE’s deformation induced by the variational magnetic field without using any external power sources. The fabricated magnetic sensor shows a fast response of 80ms and a desirable sensitivity of 31.6 mV/mT in a magnetic field range of 35–60 mT as well as preliminary vectorability enabled by the multichannel layout. Our work provides a new route for monitoring dynamic magnetic fields and paves a way for self-powered electric-magnetic coupled applications.

Dendritic copper powders are highly desirable in many applications, including electromagnetic interference shielding and conductive pastes, because of low cost and high conductivity. We prepared dendritic copper powders using the galvanic displacement reaction between the Al and Cu-ions in aqueous solution. This method is very simple and spontaneous at room temperature. During the process, the morphology of the copper powders is strongly affected by several variables, such as the displacement reaction rate and the amount of hydrogen evolution due to the reduction of proton. The effect of the different composition of electrolytes to morphological changes of copper powders was investigated in this study. In addition, the effects of concentration of chlorine ion, pH, termination time, and additives were monitored, which resulted in different morphology. Considering different applications, such as sensors, catalysts, and conductive pastes, the controllability of the morphology of dendritic copper powders plays an important role in achieving high performance in desired applications.

Abnormal protein concentration levels in human body fluids, such as urine, serum etc., are considered to associate with disease states, providing essential information for the pre-clinical diagnosis. This paper presents a wireless immunoglobulin-coated magnetoelastic (ME) biosensor for fast, cost-effective detections of human serum albumin (HSA) with small sample volumes at a microliter scale. This is the first portable resonant sensor based on magnetostrictive effect that can monitor different molecular states of HSA. Anti-HSA Immunoglobulin G (IgG) was immobilized on the surface of the ME sensor to selectively capture HSA. The rapid conjugation between the antibody and antigen changed the sensor surface states and thus induced resonance frequency shifts (RFS), which were monitored in real time for the qualitative and quantitative analysis of HSA. This paper brings forward a System on Chip (SoC)-based system architecture to realize the function of RFS sampling. The performance of the portable device was validated to be comparable to that of the Vector Network Analyzer (VNA) AV3620 using different concentrations of HSA solution. The RFS were linearly proportional to the HSA concentrations in the range from 0.1 to 100 μg/mL with a linearity up to 0.998, a sensitivity of 8.70 Hz/μg.mL-1 and a detection limit of 0.039 μg/mL, indicating good feasibility of this method. Meanwhile, the response of this portable ME biosensor was quick and specific to HSA targets. This ME biosensor shows high potential to be used in diagnosing abnormal HSA.

This paper presents a new flexible magnetic field sensor based on Ag nanowires and magnetic nanoparticles doped in polydimethylsiloxane (AgNWs & MNs-PDMS) with sandwich structure. The MNs act as the sensitive unit for magnetic field sensing in this work. Besides, the conductive networks are made by AgNWs during deformation. Magnetostriction leads to the resistance change of the AgNWs & MNs-PDMS sensors. Furthermore, the MNs increase the conductive paths for electrons, leading to lower initial resistance and higher sensitivity of the resulting sensor during deformation. A point worth emphasizing is that the interaction of the AgNWs and MNs plays irreplaceable role in magnetic field sensing, so the resistance change during stretching and shrinking was investigated. The flexible magnetic field sensor based on the mass ratio of MNs and AgNWs is 1:5 showed the highest sensitivity of 24.14 Ω/T in magnetic field sensing experiment. Finally, the magnetostrictive and piezoresistive sensing model were established to explore the mechanism of the sensor.

The last several decades have witnessed the tremendous achievement of energy storage devices such as batteries and supercapacitors in the field of charging portable electronic devices. However, the frequent charging requirement and inconvenient device replacement greatly restrict the further practical application of energy storage devices in self-powered systems for human life. Great efforts have been devoted to integrating TENG with energy storage devices to provide the sustainable power supply for electronic devices. In this review article, the recent progress of flexible TENG-based self-charging power units (SCPUs) was presented. Firstly, the working modes and triboelectric series of TENG were introduced. Next, the working principle, research progress of flexible/wearable SCPUs, and strategies to improve energy conversion efficiency were also demonstrated. Finally, the main challenges that need to be overcome when designing and optimizing TENG-based SCPUs were also highlighted.

Gel electrolytes are considered to be promising candidates for the use in supercapacitors. It is worthy to systematically evaluate the internal electrochemical mechanisms with a variety of cations (poly(vinyl alcohol) (PVA)-based Li+, Na+, and K+) toward redox-type electrode. Herein, we describe a quasi-solid-state PVA-KCl gel electrolyte for V2O5·0.5H2O-based redox-type capacitors, effectively avoiding electrochemical oxidation and structural breakdown of layered V2O5·0.5H2O during 10 000 charge–discharge cycles (98% capacitance retention at 400 mV s–1). With the gel electrolyte, symmetric V2O5·0.5H2O-reduced graphene oxide (V2O5·0.5H2O-rGO) devices exhibited a volumetric capacitance of 136 mF cm–3, which was much higher than that of 68 mF cm–3 for PVA-NaCl and 45 mF cm–3 for PVA-LiCl. Additionally, hybrid full cells of activated carbon cloth//V2O5·0.5H2O-rGO delivered an energy density of 102 μWh cm–3 and a power density of 73.38 mW cm–3 over a wide potential window of 2 V. The present study provides di...

Two steps of wet chemical processes have been developed for the preparation of core-shell nanostructures of copper and silver, which is a facile and low cost method for the production of large quantity of dendritic powders. First step involves a galvanic displacement reaction with hydrogen evolution which is the motive force of spontaneous electrochemical reaction. To achieve the core-shell structure, silver has been coated on the dendritic copper using the galvanic displacement reaction. The dendritic silver-coated copper powders exhibit high surface-area, excellent conductivity, and good oxidation resistance. It has been found that silver-coated copper powders maintain the electrical conductivity even after annealing at 150 °C for several to tens of minutes, thus it is a promising material and an alternative to pure silver powders in printed electronics application.

The oriented synthesis of high-performance nanobelt/graphene hybrids remains a challenge by one-step environmentally friendly process for supercapacitors. Here, PEG-6000 manipulation was employed to facilitate ultra-long V 2 O 5 ·0.5H 2 O nanobelts on surface of reduced graphene oxide (rGO). As a result, due to faster and efficient electron transfer and collection, V 2 O 5 ·0.5H 2 O/rGO hybrid (rGO: 5 wt%–50 wt%) significantly enhances electrochemical capacitance for supercapacitors. Especially, introduction of 50 wt% rGO in the hybrid (denoted as 50 wt% rGO-V) exhibits a high capacitance of 649 F g −1 at a scan rate of 5 mV s −1 in a neutral KCl electrolyte. On the other hand, the hybrid material shows a high-rate capacitance of 160 F g −1 at a current density of 1 A g −1 . Additionally, capacitance retention of 93% was obtained after 600 cycles, implying excellent cycling stability in the 50 wt% rGO-V hybrid. This study is beneficial to understand synergetic effects in V 2 O 5 ·0.5H 2 O/rGO hybrid materials and even useful for oriented synthesis of hybrid materials in other energy storage devices.

A dendritic Pd–Cu electrode has been prepared by co-electrodeposition of palladium and copper with high cathodic over-potentials, in which hydrogen evolution occurred. The dendritic Pd–Cu was electrochemically de-alloyed to selectively remove copper. This de-alloyed Pd–(Cu) electrode has a dramatically increased surface-area that is appropriate for electrochemical sensor applications. Electrode characteristics for use as a non-enzymatic sensor were monitored by cyclic voltammetry and amperometry, in which detection signals for hydrogen peroxide (H 2 O 2 ) were precisely measured. The prepared dendritic Pd–(Cu) electrode demonstrated outstanding electrocatalytic activity for H 2 O 2 reduction with a detection limit of 1.78 × 10 −8 M, a wide dynamic range of 50 μM to 10 mM, and high sensitivity of 915.25 μA cm −2 mM −1 .

To overcome the drawback of low electrical conductivity within supercapacitor applications, several surfactants are used for nanoscale V2 O5 to enhance the specific surface area. Polyethylene glycol 6000 (PEG-6000), sodium dodecylbenzene sulfonate (SDBS), and Pluronic P-123 (P123) controllers, if used as soft templates, easily form large specific surface area crystals. However, the specific mechanism through which this occurs and the influence of these surfactants is not clear for V2 O5 ⋅H2 O. In the present study, we aimed to investigate the mechanism of crystal growth through hydrothermal processes and the pseudocapacitive behavior of these crystals formed by using diverse surfactants, including PEG-6000, SDBS, and P123. Our results show that different surfactants can dramatically influence the morphology and capacitive behavior of V2 O5 ⋅H2 O powders. Linear nanowires, flower-like flakes, and curly bundled nanowires can be obtained because of electrostatic interactions in the presence of PEG-6000, SDBS, and P123, respectively. Furthermore, the electrochemical performance of these powders shows that the nanowires, which are electrodes mediated by PEG-6000, exhibit the highest capacitance of 349 F g(-1) at a scan rate of 5 mV s(-1) of all the surfactants studied. However, a symmetric P123 electrode comprising curly bundled nanowires with numerous nanopores showed an excellent and stable specific capacitance of 127 F g(-1) after 200 cycles. This work is beneficial to understanding the fundamental role of the surfactant in the assisted growth of V2 O5 ⋅H2 O and the resulting electrochemical properties of the pseudocapacitors, which could be useful for the future design of appropriate materials.

Ni–Sn alloy foams with different morphologies for pseudo-capacitor applications have been prepared by electro-deposition involving a hydrogen evolution reaction. The morphology depends upon the composition of electrolytes and the electro-deposition temperature. Among the several different structures of Ni–Sn foams, one that has been prepared at 45 °C represents the best electro-chemical performance of 1313 F g−1 at 1 A g−1 and it retained up to 91% of its initial performance even after 5000 cycles of charge–discharge. This Ni–Sn foam has a planar dendrite structure with bundles of flower-like tubes, providing highly porous foam with an extremely large surface area.